Reaction of Hydroxyl Radicals with C₄H₅N (Pyrrole): Temperature and Pressure Dependent Rate Coefficients

Absolute (pulsed laser photolysis, 4–639 Torr N₂ or air, 240–357 K) and relative rate methods (50 and 760 Torr air, 296 K) were used to measure rate coefficients k₁ for the title reaction, OH + C₄H₅N → products (R1). Although the pressure and temperature dependent rate coefficient is adequately represented by a falloff parametrization, calculations of the potential energy surface indicate a complex reaction system with multiple reaction paths (addition only) in the falloff regime. At 298 K and 760 Torr (1 Torr = 1.33 mbar) the rate coefficient obtained from the parametrization is k₁ = (1.28 ± 0.1) × 10^–10 cm³ molecule^–1 s^–1, in good agreement with the value of (1.10 ± 0.27) × 10^–10 cm³ molecule^–1 s^–1 obtained in the relative rate study (relative to C₅H₈, isoprene) at this temperature and pressure. The accuracy of the absolute rate coefficient determination was enhanced by online optical absorption measurements of the C₄H₅N concentration at 184.95 nm using a value σ_184.95nm = (1.26 ± 0.02) × 10^–17 cm² molecule^–1, which was determined in this work.